Closed-Loop Square-Wave Anodic Stripping Voltammetric Analyzer for In Situ Monitoring of Labile Trace Metals in Deep-Sea Environments

Reliable in situ quantification of trace metals in the deep ocean is critically important for understanding marine biogeochemical cycles, yet remains analytically challenging due to extreme hydrostatic pressure, large temperature gradients, low analyte concentrations, and severe matrix interferences. Here, we report a closed-loop square-wave anodic stripping voltammetric (SWASV) analyzer that integrates microelectrode-array sensing, environmental regulation, and signal-stability feedback to enable quantitative trace-metal measurements under deep-sea conditions. The system combines MEMS-fabricated iridium microelectrode arrays with an in situ renewable mercury film, active dissolved-oxygen removal, temperature-normalized signal correction, and background-subtracted voltammetry, forming a closed-loop analytical workflow that continuously monitors and compensates for environmental and instrumental perturbations. Under simulated deep-sea conditions, temperature-induced signal deviations exceeding 50% were reduced to within ±10-15%, while baseline noise and drift were effectively suppressed. The analyzer was subsequently deployed during two deep-sea cruises in the western Pacific, where in situ concentrations of Zn(II), Pb(II), and Cu(II) were quantified at depths up to 1800 m. Independent validation against inductively coupled plasma-mass spectrometry (ICP-MS) showed good agreement, with deviations generally within ±15%. These results demonstrate that closed-loop electrochemical regulation provides a robust pathway toward long-term, unattended, and quantitative electrochemical observations in extreme marine environments.